Cell cycle

• Cell cycle


  Regular sequence of events that produce new cells
• Phases of the cell cycle

  • Mitosis
  • G1
  • S
  • G2
• G1 phase


  • Time gap between mitosis and the beginning of DNA replication
  • Longest and most variable part
  • Period of active RNA and protein synthesis, including protein controlling progress through cell cycle
  • Cell volume, reduced by half during mitosis, returns to its previous size
• S phase


  • Period of DNA synthesis
  • Histone synthesis and beginning of centrosome duplication
• G2 phase


  • Gap between DNA duplication and the next mitosis
  • Short phase
  • Proteins required for mitosis accumulate
• G0 phase


  • As new postmitotic cells specialize and differentiate, cell cycle activities may be temporarily or permanently suspended
• Some differentiated cells, such as those of the liver, renew cycling under certain conditions: others, including most muscle and nerve cells are terminally differentiated
• Mitogens or growth factor


  Cycling is activated in postmitotic G0 cells by protein signals from the extracellular environment; binds to cell surface receptors and triggers a cascade of kinase signaling in the cells
• Checkpoint


  Where certain conditions must be met before the cell continues cycling
• Cyclins


  A family of cytoplasmic proteins that regulates overall cyclings
• Karyotypes


  Provide light microscopic information regarding the number and morphology of chromosomes in an organism
• Retinoblastoma is a type of cancer occurring in the eyes, usually in young children
• Mitosis


  Period of cell division (Greek: mitos – thread); the only cell cyle phase visible under with light microscope; parent cell divides and each of the two daughter cells receives a chromosomal set identical to that of the parent cell
• Diploid


  Produced in mitosis
• Interphase


  Also known as the G1, S, G2 phase
• Mitosis


  1. Prophase

  2. Metaphase

  3. Anaphase

  4. Telophase
• Prophase


  • Chromosomes condense
• Metaphase


  • Chromosomes line up single file
• Anaphase


  • Sister chromatids are now called chromosomes, separates and move toward opposite spindle poles by combination of microtubule motor proteins and dynamic changes in lengths of the microtubules
• Telophase


  • Genetically identical daughter cells are produced
• Cytokinesis


  At the end of telophase, constriction of this ring produces a cleavage furrow and progresses until the cytoplasm and its organelles are divided into two daughter cells
• Meiosis


  Involves two unique and closely associated cell divisions that occurs only in cells that will form sperm and egg cells; produces haploid cells with new genetic combinations
• Meiosis


  • Early in the process, the homologous chromosome of each pair (one from mother, one from father) come together in an activity termed synapsis
  • The cells produced are haploid, union of haploid egg and sperm at fertilizatiom = new diploid cell (zygote) = new individual
• Haploid


  Produced in meiosis
• Meiosis I


  1. Late interphase - synapsis and crossing over begin

  2. Prophase I - crossing over continues, paired chromosomes condense

  3. Metaphase I - homologous chromosomes line up double file

  4. Anaphase/Telophase - homologs separate into haploid daughter cells, sister chromatids remain joined
• Meiosis II


  1. Metaphase II - chromosomes line up single file in haploid cells

  2. Anaphase II/Telophase II - sister chromatids separate into nonidentical haploid cells
• Apoptosis


  Cell death; cell suicide due to pressure/stress; cells are highly condensed and shrinks
• Progenitor cell/Stem cell


  Cell origin; forms specific cell at the last stage